The EU was intensifying diplomatic efforts Tuesday to get Ukraine's leadership and pro-Moscow rebels to the negotiating table, as the OSCE said Moscow supports a de-escalation roadmap for the crisis.

German Foreign Minister Frank-Walter Steinmeier kicks things off with an early morning visit to Kiev to support a "national dialogue" between Ukraine and the pro-Russian regions in the east, said his spokesman in Berlin.

Germany this week launches another attempt to mediate in the Ukraine crisis, pushing for dialogue between the pro-Western government and pro-Russian groups to resolve the festering and violent conflict.

Foreign Minister Frank-Walter Steinmeier will visit Ukraine on Tuesday to support a "national dialogue" between Kiev and the pro-Russian regions in the east, said his spokesman in Berlin.

NATO's deputy chief vowed Monday to strengthen the alliance's partnership with Moldova during a visit in the former Soviet country that could inflame tensions with Moscow.

NATO's deputy secretary general Alexander Vershbow wrote on Twitter the alliance is "committed to enhance partnership (with) Moldova in full respect of its neutrality, supporting its independence, integrity and sovereignty."

The self-proclaimed head of the "People's Republic of Donetsk" in eastern Ukraine on Monday declared the region a sovereign state and asked Russia to consider allowing it to accede.

"Proceeding from the expression of the will of the people of the Donetsk People's Republic and in order to restore historical justice, we ask the Russian Federation to consider the issue of the Donetsk People's Republic becoming part of the Russian Federation," Denis Pushilin told reporters.

The European Union ramped up sanctions over the Ukraine crisis on Monday, adding two Crimean firms and 13 people to an existing blacklist, EU diplomats said.

No details were immediately available, but sources said the targets agreed by EU foreign ministers included two Crimean firms expropriated following the much-condemned annexation of the peninsula by Russia in March.

French President Francois Hollande said in Azerbaijan Monday that cooperation between Europe and ex-Soviet countries should not be seen as infringing on anyone else's interests, a clear reference to Moscow amid the crisis in Ukraine.

"The European Union's Eastern Partnership is not directed against anyone, but should encourage greater trade and investment", the French leader said after meeting with Azerbaijani counterpart Ilham Aliyev.

Russia raised the stakes in the Ukraine crisis on Monday by saying it respected what rebels claimed was a resounding vote in favor of self-rule in the east of the country.

But the Kremlin also called for dialogue between authorities in Kiev and rebel leaders, as European Union ministers prepared to meet in Brussels to consider toughening sanctions on Russia.

Pro-Russian rebels claimed voters in eastern Ukraine massively backed independence in a disputed poll that Kiev and the West dismissed as an illegal "farce", with complete results awaited Monday.

A total of 89 percent of voters cast ballots in favour of self-rule in the Donetsk province, one of two regions holding "referendums" on Sunday, according to the insurgents' self-styled electoral commission.

French Foreign Minister Laurent Fabius has ruled out going to war with Russia over Ukraine, but warned more sanctions will be leveled against Moscow if it tries to undermine the May 25 presidential vote.

"We cannot accept the annexation or the fact that Ukraine would be controlled or invaded," Fabius, who visits the United States this week, said in an interview published Sunday in The Washington Post.

Russia's interest in Ukraine is for "short-term gain," and its troops remain massed along the Ukrainian border, U.S. Pentagon chief Chuck Hagel said in an interview that aired Sunday.

Speaking on ABC's "This Week" Hagel qualified Russia as an "adversary in Ukraine," but stopped short of calling it an enemy.